1. Technical Field
Example embodiments of the present invention relate in general to a data transmission method for a detached machine type communication (MTC) device, whereby downlink (DL) data is effectively transmitted to the detached MTC device, in a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE)-Advanced mobile communication system providing an MTC service, and a mobile communication system providing an MTC service.
2. Related Art
In conventional mobile communication systems, terminals are generally used for human-to-human (H2H) communication. However, MTC in LTE-Advanced systems has lately been actively researched as a new application.
MTC or machine-to-machine communication (M2M) is a form of data communication which involves one or more entities that do not necessarily need human interaction. A service optimized for MTC differs from a service optimized for H2H communication. In comparison with a current mobile network communication service, the MTC service can be characterized by a) several market scenarios, b) data communications, c) lower cost and less effort, d) a potentially larger number of communicating terminals, e) a wider service area, and f) very low traffic per terminal.
MTC may be implemented in various forms of service, for example, smart metering, tracking and tracing, remote maintenance and control, and e-health.
Lately, 3GPP has also been working on MTC standardization for intelligent communication between a human and an object and between objects. For various types of MTC applications having main functions of smart metering, remote control, etc., a huge number of MTC devices are disposed and managed. In the case of smart metering, an MTC device periodically transfers measurement information, or transmits measurement information to a designated MTC server in a network when the MTC server requests the information. The number of MTC devices is far greater than that of general (H2H) terminals, but in most cases, a small amount of data is transmitted at only a specific point in time.
In 3GPP LTE systems, either of an MTC device and general user is treated as one terminal and needs to be individually registered in an LTE-Advanced network. The disposition of multiple MTC devices causes scheduling competition for channel allocation, exhaustion of radio resources, overload resulting from signal generation, and so on, thereby exerting a bad influence on existing general users. With an emphasis put on minimization of the adverse effects caused by the disposition of MTC devices, 3GPP has been working on standardization.
States of a terminal in a mobile communication system are generally classified into an attached state and a detached state. A terminal in the detached state has not been registered in a network, and the network cannot track the terminal. Due to characteristics of a providing service, an MTC device has far more cases of being maintained in the detached state than a general terminal. However, current LTE-Advanced systems do not support DL data transmission to a detached terminal. Thus, when a plurality of MTC devices are in the detached state and an MTC server requests DL data transmission to an MTC device, it is impossible to properly transfer DL data.